UvsW is a T4 bacteriophage helicase and is a member of the super family 2 (SF2) helicases. The enzyme governs the mode of replication initiation by unwinding RNA transcripts (R-loops);participates in branch migration activity, unwinds DNA substrates resembling recombination intermediates and stalled replication forks;and possesses strand annealing activity necessary for catalyzing replication fork regression. Consequently, studies on the mode of action of UvsW promises deep insights into key DNA repair processes. In this proposal the specific aims focus on defining the ATP dependent ssDNA translocation and helicase activities of the enzymes. The approach features pre-steady state ensemble and single molecule studies to determine kinetic rates, step size per ATP hydrolyzed, and processivity. The collective data should enable the formulation of a kinetic scheme for translocation and unwinding. By combining the results of parallel structural studies of the helicase with bound substrates a valuable understanding of the mechanochemistry of helicases in general should be realized. PUBLIC HEALTH RELEVANCE: Helicases are enzymes whose activities are essential to DNA replication, homologous recombination, D-loop strand invasion and replication for restart. In so far as these events are central to cell division in how helicases in particular function in normal and diseased states is of critical importance.